1. Field of the Invention
The present invention relates to a granulating and coating technique, and more particularly to a technique in which a rotary drum containing powdery or granular material therein is rotated on its substantially horizontal axis for granulating and/or coating the material.
2. Related Art Statement
In general, such a granulating and coating apparatus is operated as follows; powdery or granular material is entered into a rotary drum called a coating pan, the rotary drum is rotated, and, if necessary, coating solution etc. is sprayed into the rotary drum, or hot air or a cooling gas, for example, is supplied into and exhausted from the drum while the drum is rotated.
However, some technical difficulty arises in supplying or exhausting a gas into or from the rotary drum because the drum moves rotatively.
For overcoming the difficulties, in prior arts, the apparatus has been designed to comprise a disk valve mechanism provided on a boundary between a rotary section and a non-rotary section of a rotary drum, said disk valve having a rotary disk and a non-rotary disk, vent holes being formed on both the rotary disk and the non-rotary disk, said vent holes selectively communicating with each other at given positions so as to switch a gas supply or exhaust path. As an example, the Japanese Patent Publication No. 50-38713 discloses such a construction.
The conventional granulating and coating apparatus, however, provides the disk valve mechanism on a rear surface of the rotary drum, that is, an opposite side to an operating side. It brings about some difficulty when an operator checks for, removes, washes, or makes sure of if the disk valve mechanism is washed up.
Further, the disk valve mechanism is fixed in the axial direction of the rotary drum, therefore, the conventional apparatus has an additional disadvantage in that it is inconvenient or difficult to find out dirt on the disk valve mechanism, wash and makes sure of if the mechanism is washed out, or check for the mechanism.
The other technical object in a granulating and coating apparatus is to perform efficient stirring and mixing of powdery or granular material contained in the rotary drum for achieving efficient and uniform granulation and/or coating.
To attain this object, a proposal has been offered that the rotary drum is provided with a fixed baffle member served as an obstacle therein (Japanese Patent Publication No. 52-10665).
However, the fixed baffle member can be used only in a small apparatus because powdery or granular material slips. Further, this baffle member merely has a limited effect.
Furthermore, since the fixed baffle member is fixed on its mount position, it can not adjust to variation of the amount of the material contained in the drum.
And, as the fixed baffle member is always mounted, its presence brings about a shortcoming when the baffle member is not desired or it should not be used, or when the baffle member is to be washed out.
Moreover, the fixed baffle member may become contaminated as a result of intrusion of powdery or granular material between the inner surface of the drum and the baffle member itself, or it is hard to remove powdery or granular material between the drum and the baffle means. In particular, in case of medicines or foods, it causes a problem relating to GMP or defects of products.
Still further, in this type of granulating and coating apparatus, it is required to optimaly control conditions for processing material to be granulated and/or coated in the rotary drum to obtain an excellent product. These conditions include spraying quantity of coating solution, an amount of hot air or a cooling gas supplied to and exhausted from the drum, and temperatures of the air or the gas supplied and exhausted. Hence, it is necessary to select a parameter or parameters for the optimal control.
The conventional apparatus normally employs the methods of measuring the exhaust air temperature from the rotary drum and controlling the amount of sprayed solution based on the measured result, because it is easy to measure the temperature of the exhaust air.
Yet, though the exhaust air temperature of the rotary drum relatively corresponds to the processing temperature within the rotary drum, the former means the temperature of the gas exhausted out of the rotary drum system, and strictly, it does not directly represent an exact temperature of material to be processed or a product contained in the rotary drum. The inventors of the present invention found out that the optimal control of the foregoing conditions can not be sufficiently achieved on the basis of the exhausted air temperature.
Another conventional granulating and coating apparatus has proposed that a porous rotary drum is provided so as to supply or exhaust a gas into or out of the rotary drum through a lot of holes formed on the drum itself.
The porous drum, however, is easy to become contaminated since powder from the powdery or granular material adheres to the insides of the holes or the outer peripheral side of the drum. The contamination from these adhered powder may bring about a quite serious problem in case of granulating and coating medicines, foods, or chemicals. It is therefore necessary to certainly prevent the contamination.
On the other hand, this type of apparatus is required to keep as wide a porous area of the porous drum as possible to increase the amount of air passed through.
In order to meet with these requirements, Japanese Patent Laid-Open No. 60-71032 discloses a rotary drum including a porous polygon drum body and removable sieve elements, said drum body at least being provided with individual opening areas closely formed on the peripheral surface thereof and enclosed by a frame, and on each of said opening areas, the sieve element being mounted removably.
The foregoing drum structure, however, has some difficulty in fitting each sieve element to the frame at each opening area because of, for example, a production error. And, the fitting operation is quite troublesome.
Further, since the sieve element and the frame require the quite strict production conditions, the production becomes severe and is subject to high cost.
In addition, it is difficult to say that the drum structure makes it possible to easily check for dirt on the outer peripheral side of the sieve element or wash them out.